A powertrain is the assembly that operatively couples an internal combustion engine or similar prime mover to the driven elements, referred to the load, that are powered by the engine. Powertrains are integral parts of many mobile and stationary machines including, for example, earth moving machines, generator sets, and any other suitable type of engine-powered machines. Powertrains include different components and devices to transmit the rotational motion output from the engine and to adjust the speed, power, and/or direction associated with the motion. For example, to address operational speed and power disparities that may exist between the running engine or prime mover and the driven elements, powertrains may include components like transmissions, which have engageable gears arranged in selectable fixed ratios to increase or decrease speed, and may include torque converters. Torque converts are devices that can provide physical separation between the prime mover and the remainder of the powertrain by forming a fluid coupling between the components. Physically, the torque converter typically includes two rigid, independently rotatable parts, referred to as an impeller and a turbine respectively, that are disposed in a closely spaced arrangement with respect to each other and that are enclosed within a housing that is filled with hydraulic fluid or the like. Rotation of the impeller due to the rotational power input from the engine or prime mover causes the hydraulic fluid to flow within the housing in a manner that forces the turbine to similarly rotate, thereby transmitting power to the driven elements. Torque converters typically include an additional rigid device, referred as a stator, also disposed within the housing that assists in directing the flow of hydraulic fluid in a manner to improve transmitting speed and power through the converter.
Because fluid transmits the rotational motion through the torque converter, the impeller and the turbine can rotate at different respective speeds, an occurrence referred to as slipping or slippage. The hydraulic fluid can dissipate the difference in rotational speed between the impeller and the turbine as friction and heat. This allows the prime mover and the driven elements to rotate at different speeds and, in fact, can completely decouple the prime mover from the driven elements so the prime mover does not stall if the driven elements need to remain stationary. Accordingly, a mobile machine can come to a stop while the engine continues running. However, in many situations, it is desirable to rotate the impeller and the turbine at the same rotational speed and slippage between the components results in efficiency losses. Accordingly, torque converters are often operatively associated with a lockup clutch that can form a rigid, mechanical linkage between the prime mover and the driven elements to improve power transmission efficiency in the powertrain. To actuate the lockup clutch, it may be associated with the same hydraulic system that directs hydraulic fluid to the components of the torque converter. The present disclosure is directed to such a hydraulic system.